Single aerosol trapping with an annular beam: improved particle localisation

Area of Science:

• Optical trapping
• Aerosol science
• Beam shaping

Background:

• Optical tweezers commonly use Gaussian beams for trapping particles.
• Previous modeling suggested annular beams could improve aerosol trapping efficiency.
• Experimental verification of these theoretical predictions is needed.

Purpose of the Study:

• To experimentally investigate and quantify the advantages of using annular beams for aerosol droplet trapping.
• To compare the performance of annular beams against conventional Gaussian beams in optical tweezer setups.
• To analyze the impact of annular beams on droplet stability and trap stiffness.

Main Methods:

• Formation of an annular beam by modifying a Gaussian beam.
• Experimental trapping of aerosol droplets using both annular and Gaussian beams.
• Theoretical modeling to confirm experimental observations, focusing on axial scattering forces.
• Back focal plane interferometry to measure axial and lateral trap stiffnesses.

Main Results:

• Annular beams successfully trap smaller aerosol droplets than Gaussian beams.
• Droplets can be trapped at higher laser powers with annular beams, showing reduced axial displacement.
• Theoretical analysis confirms reduced axial scattering forces contribute to improved trapping.
• A significant increase in the axial to lateral trap stiffness ratio was observed with annular beams.

Conclusions:

• Annular beams offer superior performance for aerosol droplet trapping compared to Gaussian beams.
• The enhanced trapping is attributed to reduced axial scattering forces and improved stiffness ratios.
• This work validates the potential of annular beams for advanced optical tweezer applications involving aerosols.